Experimental investigation of heat transfer at an air‐Earth interface

Abstract

This paper is concerned with the instrumentation for, and the results from, an experimental investigation of heat transfer over a smooth dry‐lake. The original data are on file in the Department of Engineering, University of California, Los Angeles. Heat‐transfer rates into the ground were measured with thermopile heat meters; the net radiant exchange at the Earth's surface was measured with a net exchange radiometer. A continuous 48‐hour record of these quantities, together with vertical convective heat‐transfer rates determined from heat balances at the surface, is presented. Unit convective conductances (heat‐transfer coefficient's) are calculated from the convective transfer rates and differences between the surface temperature and the air temperature at a height of two meters. An empirical expression for the convective conductance, which agrees within ten per cent with the experimentally determined values, is presented.A series of small thermocouples was used to measure the air‐temperature distribution very close to the surface. Vertical convective heat‐transfer rates calculated from these measured temperature gradients compare favorably with those from the heat balances. These measurements indicate the probable existence of a laminar sublayer, though further data are necessary for conclusive affirmation.